It is required to detect the phase/frequency of a power line in various application fields, such as mains frequency monitoring, phase-controlled rectification, and mains phase detection in a power line carrier communication.
A zero-crossing detection method is employed by conventional mains phase/frequency detection, i.e., a zero-crossing point is detected by a comparator, and a cycle and a frequency of the mains are then obtained by calculating the time interval between zero-crossing points. Such method has the advantage of a high detecting speed, simplicity and reliability. However, since there is a large amount of noise and interference on the power line, the appearing time of the zero-crossing points will be affected, which thus causes it is impossible to obtain a detecting result with a high precision from such a simple zero-crossing detection method.